Flying the – 4 milliwatt – flag for piezo/solar renewables

Combining flexible solar cells with a technology known as piezoelectric strips, scientists at the University of Manchester have created a flag which can generate energy from movement in the wind, as well as from sunlight.

The flags, described in the paper Simultaneous wind and solar energy harvesting with inverted flags, published in the journal Applied Energy, can generate 3-4 milliwatts (mW) of electric power, which the researchers say could power remote sensor technologies for functions such as monitoring pollution or heat.

“Under the action of the wind, the flags we built bend from side to side in a repetitive fashion, also known as limit-cycle oscillation,” said lead author of the study Jorge Silva-Leon. “This makes them perfectly suited for uniform power generation from the deformation of piezoelectric materials.”

The team found combining the two generation technologies brought several advantages. “The solar panels bring a double benefit,” said Silva-Leon. “They act as a destabilizing mass which triggers the onset of flapping motions at lower wind speeds, and of course are able to generate electricity from the ambient light.”

The researchers also noted wind and solar generation tend to complement each other – an idea which has been put into practice at much larger scale. “Wind and solar energies typically have intermittencies that tend to compensate each other,” says co-author Andrea Cioncolini. “The sun does not usually shine during stormy conditions, whereas calm days with little wind are usually associated with shiny sun. This makes wind and solar energies particularly well suited for simultaneous harvesting, with a view at compensating their intermittency.”

The devices were tested in a range of wind speed conditions and levels of light exposure, and were found to generate up to 4 mW, which the researchers said means they could theoretically be used to power devices such as remote sensors – although no information was given about the cost of producing such devices. The researchers plan to work on boosting output to make their flag suitable for other applications.

“Our piezo solar inverted flags were capable of generating sufficient power for a range of low power sensors and electronics that operate in the microwatt to milliwatt power range within a number of potential practical applications in avionics, land and sea remote locations and smart cities,” said co-author of the paper Mostafa Nawaby. “We hope to develop the concept further in order to support more power-demanding applications, such as an eco-energy generating charging station for mobile devices.”